Gas turbine engine discharge nozzles may include variable area flaps. These flaps must tolerate high exhaust gas temperatures on the order of 4500 F during operation. It is conventional to supply a liner and cooling air to protect the underlying structure from the high temperature gases.
While relatively massive liners have been used in the past, attempts also have been made to establish thin metal liners. These have the advantage of lightweight and minimum thermal and pressure stresses due to bending.
Airfoils for a gas turbine engine have a similar problem in operating in a high temperature environment. It has been known to direct cooling air within hollow airfoils and to pass this air through openings in the airfoil to cool the surface. U.S. Pat. No. 4,653,983 shows diffusion openings with an elongated metering hole followed by a three-dimensional diffusion area, all arranged at an angle with the exterior surface. Such openings have been found to be effective in cooling the surface of the gas turbine airfoils.
While the resulting airflow conditions of such airfoils would be desirable in liners, it has not been found possible to locate such openings in thin walls. In U.S. Pat. No. 4,773,593 an arrangement is suggested to emulate such openings. Trapezoidal depressions were placed in the liner with the trapezoid becoming wider in the directional flow, and with the surface of the trapezoid being located at an angle with respect to the plane of the liner of between 5 degrees and 20 degrees. A metering airflow opening was placed at the upstream end of this depression directing airflow onto and along the surface of the depression.
Such an arrangement did lead to improved cooling over the prior art. It, however, seems that the cooling airflow does not sufficiently spread out, and that some of the hot gas is ingested into the depression. This is possibly because of the low static pressure of the relatively high velocity jet immediately downstream of the metering opening.
It is an object of this invention to achieve a diffused flow of cooling air through a thin liner in a manner which achieves increased cooling of the hot surface of the liner.